Rapid precipitation in an Al0.5CrFeCoNiCu high entropy alloy

The effect of cooling rate on the microstructural evolution of Al0.5CrFeCoNiCu has been studied using differential scanning calorimetry and scanning electron microscopy. As cast Al0.5CrFeCoNiCu contained three phases; Cr–Fe–Co–Ni solid solution dendrites, Cu rich interdendritic material and L12 precipitates. During cooling at rates between 10 and 50°C min−1, an additional exothermic event, at ∼1010°C, was observed in the heat flow curves. Microstructural examination after cooling revealed the presence of two distinct populations of intragranular precipitates not present in the as cast material. Energy dispersive X-ray spectroscopy indicated that Cu rich precipitates formed within the dendrites, while a Cr–Fe–Co rich phase formed in the interdendritic constituent. Precipitation during cooling at rates approaching 1°C s−1 indicates that the diffusion kinetics of Al0.5CrFeCoNiCu is not, as previously suggested, sluggish.